FLARE STACK ANALYSIS AND EMISSIONS CONTROL UNDER THE NEW MACT REGULATIONS
AUTHORS: DAVID FAHLE, SERVOMEX ' S HYDROCARBON PROCESSING MARKET SECTOR MANAGER AND ZARINA STANLEY, GLOBAL MARKETING MANAGER HYDROCARBON PROCESSING
MEASURING EFFICIENT COMBUSTION
The excursion of gases from a flare stack can be very quick, inconsistent, and made up of a variety of components. This is particularly the case in petrochemical plants, making them harder to monitor than refineries.
The steam-to-vent-gas ratio required can be very different for each gas- for example ethane requires 0.1 to 0.15 kg of steam per kg of gas, whereas butadiene requires the ratio to be nine times higher, between 0.9 to 1.0 kg.
Efficient regulation therefore needs continuous compositional analysis to ensure the steam-to-vent-gas ratio is maintained at its most efficient level and complies with the CE target. A device capable of this continuous compositional analysis can therefore provide a much better understanding of the overall flare performance.
Three technologies exist to help measure the efficiency of flare stack combustion: Gas Chromatography, Calorimetry, and the innovative Tunable Filter Infrared technology used in Servomex’ s SpectraScan 2400 / H2Scan system.
Gas Chromatography( GC) has been used extensively in the past, as it meets measurement requirements for most flare applications. However, GC has an issue with cycle time: a complex analysis can take up to 15 minutes. Also, temperature, density and flow can all affect GC measurements.
A calorimeter works in a different way, by burning the sample and taking a measurement of the temperature. However, it does not inform you what the composition of the sample may be. While the reading can be continuous, there is also some latency.
Servomex’ s system, comprising the SERVOTOUGH SpectraScan 2400 and H2Scan working in combination, gives a continuous reading with a good compositional measurement. It measures 14 components, giving an overall British Thermal Unit( BTU) value and individual component values.
This completely integrated system has no carrier gas and needs no recalibration or adjustment, so there are few, if any, parameters to affect the sample.
The SpectraScan 2400 is a Tunable Filter Infrared analyzer which can accurately separate light hydrocarbon components in the C1 to C6 range. With a unique wavelength-scanning spectrometer, fast analysis is performed for these light hydrocarbons, as well as H 2S if required.
Sampling is made continuously using a flow-through system, which makes it suitable for online, unattended operation, while the analyzer, having no carrier gas or recalibration requirements, does not need high maintenance.
The H2Scan integrates simply with the SpectraScan, using non-depleting thin film technology to provide a direct, realtime hydrogen measurement that is not cross-sensitive to other gases. Hydrogen is commonly vented more than any other gas, so is always present in flare lines.
The combination of these two technologies provides a detection system that is simpler and superior to traditional analysis, with considerably lower implementation and product lifetime costs.
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